Primary ignition vs injector current

The purpose of this test is to monitor the current draw from an injector whilst observing the primary ignition trace.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.


Note: This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

How to perform the test

  1. Connect a 10:1 attenuator to channel A of PicoScope.
  2. Connect channel A to the negative terminal on the ignition coil and to earth.
  3. Connect a low amp current clamp to channel B of your PicoScope.
  4. Select the 20 A scale and zero the clamp before clamping around the injector supply cable.
  5. Start the engine and run at idle.
  6. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  7. Start the scope to see live data.
  8. With the live waveforms on screen stop the scope.
  9. Turn the engine off.
  10. Use the Waveform Buffer and Zoom tools to examine your waveform.

Example waveform

Waveform notes

In this waveform we can observe the current drawn by the injector (shown in red) at the same time as monitoring the primary ignition trace (shown in blue). 

Example ignition coil

Example multi-point petrol injector

Further guidance

The main reason for evaluating these two waveforms together is to identify the cause of a non-start situation or sudden loss of power, causing the engine to stop.

If the primary trace is absent, there will be no switching of the injectors as these two circuits are timed together while the loss of the injector current signifies that a fault has occurred within the injection circuit.

The frequency of the injection trace when compared to the primary signal will differ between sequential and simultaneous injection. Sequential having one pulse per 720, while simultaneous will predominantly have two. Some simultaneous systems do however have a single pulse, but these are in the minority.


Please see individual waveform topics:

  • Ignition primary
  • Multi-point injector current


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • 20 A / 60 A DC (low amps) current clamp


  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Primary ignition vs injector current